In LCD panel production, to improve production efficiency, plural LCD panels are formed on a large mother panel, then they are separated from the mother panel by scribing. Generally, for glass cutting, a wheel made of, for example, sintered diamond or cemented carbide with a diameter of several millimeters is used. The wheel has a circumferential edge and is moved on a glass surface while applying a certain pressure to the glass surface. The wheel moves on the glass surface cutting into the glass by several micrometers thereby forming a linear score measuring several micrometers both in depth and in width. Such a linear score may hereinafter be referred to as a “fracture layer.”
At the same time as the linear score is formed, a crack with a depth vertical to the glass surface of several tens of micrometers to several hundred micrometers is formed immediately below the linear score. The formation of such a vertical crack propagates, as the wheel advances, ahead of the advancing wheel position with a front angle of several degrees with respect to the vertical direction extending right below the wheel. That the formation of the vertical crack propagates with such an angle can be known by observing a mark called a rib mark which is generated on the cut surface of the glass. The depth of the vertical crack is the depth of the rib mark plus the depth of a crack formed to further extend depthwise beyond the rib mark. As far as the present invention is concerned, the rib mark depth and the depth of the vertical crack may be regarded, for the sake of convenience, as being identical. Generally, the operation and what is caused by the operation described above are collectively referred to as scribing. To separate a sheet of glass into multiple parts, one side of a sheet of glass is scribed, and the scribed portion is pressed from the other side causing the vertical crack formed in the scribed portion to extend deeper. This glass separation may be referred to as breaking.
FIG. 22 shows a glass cutter 1. As shown, the glass cutter 1 includes a wheel 10 used for scribing, a wheel pin 11 serving as a shaft of the wheel 10, and a holder 12 supporting the wheel 10 and the wheel pin 11.
FIG. 23 is a sectional view of the wheel 10 used for scribing. Referring to FIG. 23, the wheel 10 has a ridge, i.e. a cutting edge 101, bevels 102, and sides 103. The wheel 10 has thickness t ranging from 0.5 to 1.0 mm, edge angle θ ranging from 100 to 130 degrees, and diameter d ranging from 2 to 3 mm. The wheel 10 is formed of, for example, sintered diamond or cemented carbide.
FIGS. 24A and 24B are a plan view and a sectional view, respectively, showing scribing of glass performed using the wheel 10 shown in FIG. 23. Referring to FIG. 24A, a fracture layer 201 formed by the wheel 10 has width w which is about several micrometers.
Referring to FIG. 24B, the fracture layer 201 formed by the wheel 10 has depth d1, and a rib mark 202 is formed below the fracture layer 201 with a crack 203 further extending from the rib mark 202. Depth d1 of the fracture layer 201 is several micrometers. Depth d2 from the glass surface to the bottom of the crack ranges from several tens of micrometers to several hundred micrometers.
In FIG. 24B, a white arrow MD denotes the moving direction of the wheel 10, “FF” denotes a force moving the wheel 10, and “RF” denotes a rotating force generated as the wheel 10 moves. Also, “F1” denotes a force the wheel 10 applies, in its moving direction, to the glass 300; “F2” denotes a force the wheel 10 vertically applies to the glass 300; and “F3” denotes a resultant force of F1 and F2. As the wheel 10 moves, while rotating, in the direction MD, the crack 203 is formed in the glass 300.
The above glass cutting mechanism is described, for example, in literature by Toshihiko Ono and Yuko Ishida, “Cuttability of AMLCD Glass Substrate” in SID 02 DIGEST, pages 45-47 (2002) and also in literature by T. Murata, S. Miwa, H. Yamazaki, S. Yamamoto, “Suitable Scribing Conditions for AMLCD Glass Substrate” in SID Digest, pages 374-377. Also, a configuration for stably forming a crack when forming a scribe line crossing an existing scribe line on a glass surface is described, for example, in Japanese Patent Laid-Open No. 2009-93051. Furthermore, a wheel 10 with notches formed on its cutting edge so that it may securely rotate on the glass surface is described in WO2007/004700. Still furthermore, a configuration in which a wheel 10 and a rotary shaft for rotating the wheel 10 are united is described in Japanese Patent Laid-Open No. 2001-246616.